You won't get television-quality video with an inexpensive Webcam; you'll get small fuzzy herky-jerky. But it's acceptable herky-jerky. A low-end Webcam typically supports 15 frames per second at 320 x 240 pixels. For comparison, movies run at 24 fps. Spending a bit more money will get you some silky smooth video. One example is the Logitech QuickCam Pro 9000. For $99.99 you get a built-in microphone, autofocus, good-quality optics, 30 frames per second, and high-quality video capture size up to 960 x 720 pixels.
It takes more than a good Webcam to get good performance. You should have a modern PC, dual-core if possible, because all that video processing takes some horsepower. A typical minimum bandwidth requirement for smooth video is 256 kbps both ways.
Linux support for Webcams is pretty good, thanks to a number of hardy Linux developers. As usual, the vendors themselves have no interest in supporting anything but MS Windows. Michel Xhaard, with little help, figured out how to support over 250 different Webcams from a common base driver. This base driver, GSPCA/SPCA5xx, is now included in Debian and its offspring. The good folks at Linux UVC driver and tools support a different set of Webcams, and the nice people at Philips USB Webcam Driver for Linux keep it maintained, even though it supports mostly older devices.
The bad news is "pretty good" means you may still have to compile and manually install drivers, and perform other manual tweakages. Just like the good old days.